1. Field of the Invention
The present invention relates, in general, to a method of constructing partially earth-anchored cable-stayed bridges using a thermal prestressing technique and, more particularly, to a method of constructing partially earth-anchored cable-stayed bridges using a thermal prestressing technique, in which, while a steel girder-type partially earth-anchored cable-stayed bridge is built using a cantilever construction technique, the center of an intermediate span of the bridge is closed with a final key segment using a thermal prestressing technique, thus applying an appropriate initial axial tensile force to reinforcing girders of the bridge.
2. Description of the Related Art
In recent years, as bridges for spans of about 200˜1000 m, cable-stayed bridges have been recognized as appropriate structures having good appearances and providing high economic efficiency. However, according to the lengthening of the spans, the cable-stayed bridges are problematic in that an excessive compressive force is applied to the upper structure of the bridges, so that buckling may be caused in the towers of the bridges.
In an effort to solve the problems of the conventional cable-stayed bridges, a partially earth-anchored cable-stayed bridge, in which an initial tensile force is artificially applied to the reinforcing girders of the bridge so as to reduce the excessive compressive force from the upper structure of the bridge, has been studied and proposed. However, in the related art, there has been no appropriate construction technique of applying tensile force generated using outside anchor cables to an intermediate span of a bridge in a process of closing the center of an intermediate span of the bridge with a final key segment, so that the partially earth-anchored cable-stayed bridge has not actually been built and put to practical use anywhere in the world.
Here, the technical term “final key segment” has the following meaning. That is, in a cantilever construction process of building a cable-stayed bridge by constructing two support towers and by gradually extending reinforcing girders from the two towers, the final key segment is a final closure element to couple the reinforcing girders to each other at the center of an intermediate span between the two towers while compensating for construction error generated between the reinforcing girders separately and respectively extending from the two towers. The coupling of the two reinforcing girders using the final key segment is so-called “closure of the final key segment” in the related art, and the step of closing the junction between two reinforcing girders with a final key segment has been recognized as the most important step in the process of building a cable-stayed bridge using a cantilever construction technique.
In a conventional technique that can be adapted to a process of building a partially earth-anchored cable-stayed bridge requiring an appropriate initial tensile force to be applied to reinforcing girders, excessive compressive force is applied to the reinforcing girder of the cable-stayed bridge (a so-called “self-anchored cable-stayed bridge”) due to the long span of the cable-stayed bridge, so that the bridge must be designed such that the reinforcing girders have a large sectional area in proportion to the excessive compressive force. Furthermore, at the step of closing the junction between the reinforcing girders of the intermediate span with a final key segment in the conventional technique, the facing ends of the reinforcing girders of the intermediate span must be prestressed with an appropriate tensile force using prestressing machines, such as hydraulic jacks, prior to closing the junction between the reinforcing girders with the final key segment.
In other words, in a conventional technique of closing the junction between the reinforcing girders at the center of the intermediate span with a final key segment, the reinforcing girders are prestressed using hydraulic jacks and provide an appropriate space for the closure of the final key segment. However, to close the junction between the reinforcing girders with a final key segment using the conventional technique, a plurality of prestressing anchors must be installed at the ends of the reinforcing girders and, furthermore, the ends of the huge reinforcing girders must be prestressed with a uniform tensile force using a plurality of hydraulic jacks, and this causes difficulty in the conventional technique of building a partially earth-anchored cable-stayed bridge.
In the related art, a partially earth-anchored cable-stayed bridge may be built through a process, in which, after the junction between the reinforcing girders has been completely closed with a final key segment, cables are anchored to outside anchors and, thereafter, tensile force is applied to the reinforcing girders. However, this process is problematic in that it is almost impossible to separately anchor the cables, each comprising a great number of steel wires, to the outside anchors such that a uniform tensile force can be applied to the respective steel wires of the cables.
Therefore, in the related art, it has been required to provide a new technique of applying tensile force to the reinforcing girders of a partially earth-anchored cable-stayed bridge in an effort to solve the problems experienced in the conventional technique of building the partially earth-anchored cable-stayed bridge.